A power combining unit that obtains high output electric power by combining a plurality of electric power inputs is known as one means for obtaining an output of high electric power. This power combining unit includes a plurality of input ends to which electric power is input and an output end from which the combined electric power is output. In addition, the electric power combining/dividing unit functions as a power dividing unit if the input ends are used as an output end and the output end is used as an input end. Therefore, “a power combining unit” and “a power dividing unit” are referred to as an electric power combining/dividing unit in this specification.
Such an electric power combining/dividing unit as described above is disclosed in, for example, PTL 1. The electric power combining/dividing unit disclosed in PTL 1 includes a main body having a void therein, a central coaxial plug provided substantially at the center of the main body, a plurality of peripheral coaxial plugs, arranged concentrically about the central coaxial plug, that is installed in the main body, a radial line formed in the void in the main body, a central coaxial line having one end connected to the central coaxial plug and the other end connected to the center of the radial line, and a peripheral coaxial line having one end connected to the peripheral coaxial plug and the other end connected to the outer peripheral part of the radial line. This electric power combining/dividing unit functions as a power combining unit when the central coaxial plug is used as an output terminal and the peripheral coaxial plug is used as an input terminal or functions as a power dividing unit when the central coaxial plug is used as an input terminal and the peripheral coaxial plug is used as an output terminal.
In order to achieve combined output having high electric power, the multistage connection of the electric power combining/dividing units (the multistage connection of a plurality of electric power combining/dividing units) disclosed in PTL 1 is performed to obtain desired high output electric power.
Since a coaxial line has larger transmission loss and lower electric power resistance than a waveguide line, the cutoff frequency becomes low when a coaxial line having a large diameter is used and there are limitations in application to a high frequency band and high electric power.